For example, an atomic force microscopy device (also called MS-AFM or Mode Synthesizing Atomic Force Microscopy) is known from U.S. Pat. No. 8,448,261 that in particular describes the use of two ultrasound waves applied near a measurement probe on the one hand, and a sample on the other. However, this known technology is not without major disadvantages. Indeed, the sources of ultrasound excitation near the lever (or probe) and the sample must be installed manually for each operator using this device, which can lead to a high degree of variability of positioning of the ultrasound excitation sources near the lever, and consequently a significant variation in the measured results.
Adding a piezoelectric actuator near the measurement lever results in a path of the light beam emitted by the laser diode which, after reflection on the end of said lever, is longer and offset relative to the initial path. Indeed, the lever supports as well as the levers are designed so that after reflection, the laser beam generally arrives on the mirror in order to be sent to a photodiode (photodetector). Even if there is an angular adjustment at the mirror in order to adjust the position of the laser spot on the photodiode; this adjustment is limited. The fact of having a piezoelectric actuator near the measurement lever, which is then positioned on its support, therefore generates an offset towards the bottom of the mirror of the optical path of the reflected laser beam. It is generally possible only to partially make up for this offset by returning the spot back onto the photodiode with a limited inclination of the mirror. However, often only a portion of the power of the laser spot is returned to the photodiode. This generates a signal loss affecting the reliability of measurements, and the adjustment of the device is not optimal. Due to the extent of observed offset, it is often difficult and even impossible to correctly center this laser spot.
Moreover, during measurements in a liquid medium, this phenomenon is accentuated by the phenomenon of refraction of the light rays. This technology is therefore unusable in liquid media.
Furthermore, these devices, which often use an ultrasound or piezoelectric excitation source placed beneath the sample, prevent an additional spectrum analysis from being performed.
Also known, for example from document US 2011/0231966, is an atomic force microscopy device (also called MS-AFM) that uses two ultrasound waves, one applied near a measurement probe and the other near a sample. However, the above-mentioned disadvantages also apply to such a configuration. In the aforementioned configuration, it is essential that the sample be disposed on a support (for example on a glass or metal slide) in order to adhere the piezoelectric actuator beneath the surface of the sample. This makes it possible to ensure a satisfactory transmission of the ultrasound waves. This operation requires the use of a heated adhesive. This can induce heating of the sample. Such heating can prove harmful for biological samples.
The use of such an adhesive, for example even for cold adhering, risks altering the sample due to the presence of harmful compounds such as solvents.
Moreover, in a particularly disadvantageous manner, the piezoelectric actuators of this device are not decoupled from the measurement lever.
Also known is the acoustic measurement device based on atomic force microscopy described in document JP H08 21826 A.
Conventionally this device comprises a cantilever the end of which includes a measurement point intended to interact with the surface of the sample and the vertical oscillations of which are analyzed by means of a laser device or a piezoelectric element situated on the point of the lever.
In this known device, the sample is placed on the upper face of a conventional parallelepiped-shaped support.
During analysis, Rayleigh type surface waves are generated at the surface of the sample by means of two transducers that are each mounted on an acrylic resin support, placed on the surface of the sample.
To be able to generate such surface waves, it is therefore essential that the transducers of this device be placed on the surface of the sample. Consequently, they cannot be moved against the support of the sample, and even less so against a face of this support spaced apart from the sample.